The invention relates generally to a sealing device for a container, and more particularly, to a sealing device having a sealing capacity that varies according to the pressure in the container.
Containers such as test tubes have been used to store sample materials such as liquids. Removable caps have been used in conjunction with such tubes to prevent contamination or loss of the sample, while allowing for subsequent re-access to the sample. Typically removable caps rely on friction fit between a cylindrical portion of the cap and the inside surface of the test tube to form a seal between the test tube and cap. Such friction seal caps can be integrally formed with the tube and attached to the tube by a hinge as disclosed in U.S. Pat. No. 4,674,640. However, among the drawbacks of frictional cap seals is their inability to maintain seal integrity when dropped or subjected to heat or cold in which case the internal pressure increases and can break any hermetic seal formed between the cap and tube. As a result, the sample can evaporate, for example. In addition, substantial increases in internal pressure can cause the cap to pop off, resulting in sample loss. Although the sealing strength can be increased by increasing the friction fit between the cap and test tube, such an arrangement makes insertion and removal of the cap much more difficult (something even requiring a tool) and can result in the sample spilling when the cap is abruptly moved upon removal due to the relatively high static friction force.